1. Field of Invention
The present invention relates generally to fiber optic coupled pressure transducers and methods for their fabrication and, more particularly, to ultraminiature fiber optic pressure transducers formed with a photosensitive polymer and a micromachining technique for fabricating the same.
2. Description of the Related Art
Light intensity modulated transducers employ measurements of changes in a light signal sent to and reflected back from a moving reflective surface. In the case of fiber optic pressure transducers, light from an optical source, e.g., a light emitting diode, is transmitted through an optical fiber to a light reflective diaphragm at the fiber tip, and reflected back from the reflective diaphragm through the same fiber to a light level analysis unit. Generally, the amount of light that is reflected is determined by the distance between the reflective diaphragm and the fiber end. As the pressure on the diaphragm changes, its reflective surface is deflected toward or away from the fiber end changing the amount of reflected light in accordance with the applied pressure.
An example of such a fiber optic pressure transducer is provided in U.S. Pat. No. 4,787,396 to Pidorenko, the entirety of which is incorporated herein by reference. The disclosed pressure transducer incorporates four structural members: a fiber, a fiber-holding ferrule with an annular shoulder, a cylindrical cap with a rounded lip, and a light reflective diaphragm. The ferrule is formed from continuous, cylindrical, drawn titanium tubing which is fed through a screw machine where it is turned, a step is cut in the end to provide the annular shoulder, and then cut to length. The cap is formed from a titanium rod and drilled and bored to provide a step for the diaphragm. In the disclosed pressure transducer, the diaphragm is permanently affixed between the lip of the cap and the annular shoulder of the ferrule, at a fixed distance from the end of the fiber-ferrule assembly.
Another example of a fiber optic pressure transducer and method of fabrication is provided in U.S. Pat. No. 4,711,246 to Alderson, the entirety of which is incorporated herein by reference. The disclosed pressure transducer includes: a hollow cylindrical cap made from titanium with a diaphragm formed to its final thickness and shape by a hot coining process, and a ferrule made from drawn tubing. In the disclosed method, the ferrules are cut and loaded into a fixture plate, and then fibers are inserted into the ferrules. The plate, including the end surfaces of the ferrules and fibers, is lapped and polished in a single operation. A photoresist coating is applied to the fiber ends. A pattern of small holes is made in the resist material via exposure in a standard semiconductor alignment machine. Then, the ferrules are unloaded from the machine and ready for assembly with the caps.
A problem with the above techniques is that the structural members are fabricated separately using conventional machining. Thus, completed transducers are about 1 mm and larger in size. Moreover, the manual assembly of such structural members can be costly.
In xe2x80x9cA Fiber-Optic Pressure Microsensor for Biomedical Applicationsxe2x80x9d by O. Tohyama, M. Kohashi, M. Fukui and H. Itoh in TRANSDUCERS ""97 (1997 International Conference on Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997, pp. 1489-92), the entirety of which is incorporated herein by reference, an intensity modulated fiber optic pressure sensor including separately processed silicon wafers (diaphragm, fiber stopper and alignment structure) is disclosed. The silicon wafers are bonded together and then diced to provide individual sensing elements.
A problem with the Tohyama technique is that using wafer dicing to separate the individual sensing elements for attaching each of the sensing elements to a fiber is a costly manufacturing process. Moreover, the Tohyama technique requires complex separated processing steps, a complicated alignment procedure and special handling, thus increasing the cost and reducing the fabrication yield. Although the Toyama article discloses a completed sensing element with an outer diameter of 270 xcexcm, its sensitivity is limited by its relatively thick (50 xcexcm) fiber stopper.
Fiber optic pressure transducers hold great potential in a variety of applications for direct, accurate measurements of pressure in gases and liquids because of their wide dynamic range, high sensitivity, and an immunity to electromagnetic influence. To be successfully used in medical applications that require pressure measurements in human organs, the transducers should be made as small as possible to be inserted through small catheters and infusion needles to minimize the painfulness of medical routines. For clinical routines, it would also be very desirable for transducers to be disposable.
Thus, there is a need for a simple and reliable, low cost, batch in nature fabrication process for fiber optic pressure transducers which includes a small number of processing steps and does not require individual handling of parts during fabrication.
There is also a need to improve the sensitivity of fiber optic pressure transducers such that a single mode fiber with a core, for example, of 4-10 xcexcm, could be utilized with a comparable fiber-diaphragm distance.
The present invention is embodied in an xe2x80x9cultraminiaturexe2x80x9d fiber optic pressure transducer which is suitable for a variety of medical applications including, but not limited to, treating pressure build-up in kidneys and high blood pressure. The term xe2x80x9cultraminiaturexe2x80x9d means sufficiently small in size (about 350 xcexcm and smaller) to be inserted by a needle into the body so that, when the needle is withdrawn, the body can heal without the need for stitches, sutures or the like.
An exemplary preferred embodiment of the present invention generally relates to an ultraminiature, high sensitivity fiber optic pressure transducer structure and a batch method for fabricating the same. The pressure transducer includes a fiber-ferrule assembly and a fiber alignment assembly sized to receive the fiber-ferrule assembly. The fiber alignment (and pressure sensing) assembly includes an integrally formed diaphragm, fiber stopper and fiber alignment cavity. The fiber-ferrule assembly includes a fiber and a ferrule sized to receive the fiber therein. In an exemplary preferred embodiment, the structural members of the pressure transducer are formed with a photosensitive polymer such as an epoxy-based photoresist which provides precise alignment structures which are rigid or hard and facilitates easy and accurate fitting of the fiber-ferrule assemblies into the fiber alignment assemblies.
According to the present invention, the structural members are made by using an entirely surface micromachining technique. Completed free standing pressure sensing elements are formed on the surface of a substrate simultaneously, and then released therefrom. The fabrication method of the present invention eliminates manual handling of micro parts during the fiber assembling and releasing processes.
In an exemplary preferred method, the fiber alignment (and pressure sensing) assemblies are formed on a first substrate and the fiber-ferrule assemblies are formed on a second substrate. The structural members are formed onto the first substrate in series, one after another: the light reflective diaphragms and then the fiber stoppers and fiber alignment structures. The reflective diaphragms are formed with any desired thickness. Ferrule structures are formed onto the second substrate and then fibers are inserted into and sealed to the ferrule structures forming the fiber-ferrule assemblies. The fiber-ferrule assemblies are released from the second substrate and inserted into and sealed to the fiber alignment assemblies. The fiber alignment assemblies remain secured to the first substrate until completed transducers are to be freed therefrom. As a result of this process flow, all monolithic sensing elements are ready at the same time.
A method for making an ultraminiature fiber optic pressure transducer integrally composed of photosensitive polymer members, and a single mode fiber, in accordance with one embodiment of the present invention, includes the steps of: forming a sacrificial layer on a surface of a substrate; forming flexible light reflective diaphragms on the sacrificial layer; forming fiber stopper structures on the surface of the substrate, the fiber stopper structures being in alignment with the diaphragms; forming fiber alignment structures on the fiber stopper structures, the fiber alignment structures being in alignment with the diaphragms and the fiber stopper structures, the diaphragms, the fiber stopper structures and the fiber alignment structures serving as pressure sensing elements; forming a sacrificial layer on a surface of an additional substrate; forming ferrule structures on the surface of the additional substrate; inputting fibers into the ferrule structures including sealing the ferrules to the fibers, the ferrule structures and the fibers serving as fiber-ferrule assemblies; etching the sacrificial layer to release the fiber-ferrule assemblies from the additional substrate; inputting the fiber-ferrule assemblies into the pressure sensing elements including sealing the pressure sensing elements to the fiber-ferrule assemblies, the pressure sensing elements and the fiber-ferrule assemblies serving as fiber optic pressure transducers; and etching the sacrificial layer to release the fiber optic pressure transducers from the substrate.
A method of batch fabrication of ultraminiature fiber optic pressure transducers in accordance with another embodiment of the present invention includes the steps of: providing a first substrate with a first sacrificial layer formed thereover; forming a light reflective diaphragm structures on the first sacrificial layer; forming fiber stopper structures on the light reflective diaphragm structures; forming fiber alignment cavity structures on the fiber stopper structures, the light reflective diaphragm structures, fiber stopper structures and fiber alignment cavity structures providing a plurality of fiber alignment assemblies; providing a second substrate with a second sacrificial layer formed thereover; forming ferrule structures over the second sacrificial layer; inputting fibers into the ferrule structures and sealing each of the ferrule structures to the fiber inserted therein, the ferrule structures and the fibers providing fiber-ferrule assemblies; etching the second sacrificial layer releasing the fiber-ferrule assemblies; inputting the fiber-ferrule assemblies into the fiber alignment assemblies and sealing each of the fiber alignment assemblies to the fiber-ferrule assembly inserted therein, the fiber alignment assemblies and the fiber-ferrule assemblies providing a plurality of fiber optic pressure transducers; and etching the first sacrificial layer releasing the fiber optic pressure transducers.
In an preferred embodiment, the light reflective diaphragm structures are formed from a photosensitive polymer, a non-photosensitive polymer and/or a metal. In an preferred embodiment, the fiber stopper structures, the fiber alignment cavity structures and the ferrule structures are formed from an epoxy-based photoresist.
A method of batch fabrication of ultraminiature fiber optic pressure transducers in accordance with another embodiment of the present invention includes the step of: employing a surface micromachining technique to provide a flexible diaphragm with an integrally formed fiber alignment structure, the fiber alignment structure being sized to receive a fiber-ferrule assembly therein. In a preferred embodiment, the method further includes the step of: employing the surface micromachining technique to fabricate a ferrule structure of the fiber-ferrule assembly, the ferrule structure being sized to receive a fiber of the fiber-ferrule assembly.
A method of batch fabrication of ultraminiature fiber optic pressure transducers in accordance with another embodiment of the present invention includes the step of: employing a surface micromachining technique to provide a flexible diaphragm with an integrally formed fiber stopper structure.
An ultraminiature fiber optic pressure transducer in accordance with another embodiment of the present invention includes: a flexible diaphragm; a fiber alignment structure secured to the flexible diaphragm, the fiber alignment structure being formed with a photosensitive polymer; and a fiber-ferrule assembly sealed within the fiber alignment structure.
An ultraminiature fiber optic pressure transducer system in accordance with another embodiment of the present invention includes: a plurality of ultraminiature fiber optic pressure transducers configured to measure pressures within a plurality of pressure ranges which are different and to generate output signals for the pressure ranges; and a processor configured to receive and process the output signals.
An ultraminiature fiber optic pressure transducer system in accordance with another embodiment of the present invention includes: an ultraminiature fiber optic pressure transducer adapted to generate an output signal; and a transmitter electrically connected to the pressure transducer, the transmitter being adapted to receive and transmit the output signal.
The above described and many other features and attendant advantages of the present invention will become apparent as the invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings.